Section 232 of the Constitution provides that customary international law is law in the Republic unless it is inconsistent with the Constitution or an Act of Parliament. The provision, in its terms, is simple. Its operational consequences have been more complex, and a developing body of jurisprudence in the Constitutional Court has begun to articulate the framework within which the provision is to be applied.
Three operational questions have emerged. The first is the standard of proof for the existence of a rule of customary international law in domestic proceedings. The Court has accepted that the standard is the orthodox international law standard — general practice accepted as law — but the evidentiary requirements for establishing that standard in a domestic forum, with limited access to state practice and opinio juris, have proved demanding.
The second is the relationship between customary international law and the Bill of Rights. Where a rule of customary international law engages a right protected under the Bill of Rights, the question is how the two bodies of law are to be reconciled. The Court has indicated that the constitutional rights take precedence, but that the content of the constitutional rights may itself be informed by the relevant customary law, particularly through the interpretive provisions in section 39.
The third is the question of justiciability. Some rules of customary international law engage questions of foreign relations that the courts have traditionally treated with restraint. The Court has begun to develop a doctrine of judicial deference in respect of foreign relations matters, but the boundaries of that doctrine are still being worked out. The recent cases suggest that the doctrine operates more strongly at the level of the executive's engagement with foreign states than at the level of the determination of individual rights affected by foreign-relations decisions.